Scabies

Scabies is caused by the arachnid mite Sarcoptes scabiei. It commonly affects children and young adults, and is spread by prolonged skin contact.

• Risk factors
  • Close living conditions
  • Poor hygiene
  • Low socioeconomic status
  • Immunosuppression – increased risk of crusted (Norwegian) scabies
  • Crowded institutions, e.g. hospitals and schools
  • Tropical and subtropical regions
• Pathophysiology
  • The mite burrows into the skin and lays eggs in the stratum corneum → delayed-type IV hypersensitivity to mites/eggs → intense pruritus
• Signs and symptoms
  • Widespread pruritus
    • Worse at night
  • Papular rash
  • Linear burrows
    • Side of fingers
    • Interdigital webs
    • Flexor aspects of the wrist
    • Face and scalp in infants
  • Excoriation due to scratching
• Differentials
  • Insect bites
  • Atopic dermatitis
  • Tinea
  • Impetigo
  • Psoriasis
  • Folliculitis
  • Lichen planus
• Investigations
  • Skin scrapings
  • Adhesive tape test
  • Dermatoscopy
    • ‘delta-wing jet’ appearance
  • Biopsy
    • Burrowa containing mites, eggs, or fecal matter in the stratum corneum
  • Sarcoptes scabiei-specific PCR
• Treatment
  • Permethin 5% (first-line)
  • Malthion 0.5 % (second-line)
  • Anti-histamines, steroid creams, and/or emollients for pruritus
  • Household and physical contacts should also be treated at the same time
  • Avoid close physical contact until treatment is complete
  • Launder, iron, or tumble dry garments to kill mites
• Complications
  • Secondary bacterial infection
  • Norwegian (crusted) scabies: this is seen in immunosuppressed patients. The skin rash is hyperkeratotic and may resemble psoriatic plaques.
  • Scabies nodules
  • Ecthyma
  • Flare-up of eczema or psoriasis